Basement Jamming Bass Amp Recommendation

I was thinking of getting a new bass amp to jam some surf tunes with my 13-year old son. Previously all I had was an old 15w Crate amp, which sucks and won't do. What kind of wattage should I be aiming for if the only venue I will be using this amp in is the basement?

I have an Acoustic B20 that I really like. It's solid state so I don't have to feel sheepish about flicking in on for a minute or two to work something out like I might with a tube amp. It has four EQ knobs, which is convenient, as I use it mainly for guitar and this allows it to be dialed bright enough for that. And it gets loud! I rarely go above 1 on it for practice.

I bought it at Goodwill for 20 bucks with an unknown electrical issue that had rendered it nonfunctional and after a 5 dollar capacitor swapping session, it became one of my very favorite purchases. From my perspective, it's nice to have a guitar amp that I can also play bass through when I want but from your perspective, it might be nice to have bass amp that you can also dial in for guitar if you want.

Get a Fender Excelsior Pro. 15 watt tube amp. 15" speaker. If it is just for basement jamming it will kill at both bass and guitar. You will really like it, it's a lovely little amp. Personally, I have one and use it a lot with my Bass VI and my guitars. It's just the right power to sound good in a house but not make other occupants upset/annoyed.

I'm using a Behringer BX108. It's a pretty basic combo amp, only 15W, 8" speaker - but it's got a lovely tone and it's loud enough for a two person basement jam. Also discontinued, but unlike the Excelsior you can get one pretty affordably. ;)